1. Field of the Invention
This invention relates to the use of derivatives of tricylco-[5.2.1.0.sup.2,6 ]-dec-3-ene as frothers in the flotation of coal and ores.
2. Statement of Related Art
Run-of-the mine coal or rough coal from coal mining is widely worked up mechanically utilizing the differences in density. In the process of working up, the rough coal is mechanically separated into a coal fraction and a so-called "dirt fraction".
Flotation is preferred as a separation process, particularly for fine coal (particle size below 0.5 mm), the fine coal being separated from the ash on the basis of different surface properties of coal particles and dirt particles. To this end, use is made of the natural, water repellent character of the surface of coal particles which is enhanced by adsorption of hydrophobic reagents. In suitable media, fine coal and ash can be separated by a flotation process which is now being successfully used on an industrial scale. In the flotation process, the fine coal particles are attached to froth bubbles of a sufficiently stable froth produced by addition of a frother and discharged in this way from the flotation cell.
In principle, the criteria set forth above with respect to the flotation of coal apply equally to the flotation of ores. In this field, the valuable mineral in the ores is intended to be separated from the gang by the flotation process and the minerals enriched in the valuable mineral fraction by successive application of individual flotation steps. To this end, the ore is size-reduced and preferably wet-ground and subjected to the flotation process after addition of a frother and a collector and other chemicals necessary for or useful in the flotation process. Appropriate formulation of the pulp with respect to pH, type and concentration of the collectors and type and concentration of the frothers enables the valuable mineral to be selectively separated from the gangue in high yields. In this connection, it should be noted that an increase in the yield or selectivity by only a few percentage points through reagent combinations of different composition or improved flotation cells may be regarded as a successful improvement of considerable economic significance, because the daily throughputs in the industrial processing of coal and ores are often of the order of several tens of thousands of tons of ore. An increase of several tons in the yield of valuable mineral in an industrial flotation process is regarded as highly advantageous.
The effect of a frother, which generally consists of molecules having a polar part and an apolar part, is not confined solely to the generation of the froth. Characteristics of the froth of importance to the process, such as bubble size, bubble strength and bubble cohesion, can be controlled through the type and quantity of the frothers. Also, the frother generally influences the other constituents of the flotation pulp. The influence of the frother is undesirable when it acts non-selectively on the collectors which are intended to modify the hydrophilicity of the particle surface and to provide for better adhesion of the particles to the froth bubbles. Accordingly, it has hitherto been desirable to use only those frothers of which the properties only affect the stability and strength of the froth and, in addition, provide for minimal consumption, but do not affect other parameters of the process (cf. Ullmanns Enzyklopadie der technischen Chemie, 4th Edition, Verlag Chemie, Weinheim (1972), Vol. 2, page 110 et seq.).
According to "Ullmann" loc. cit., frothers for flotation processes are not intended to possess any structures which lead to parallel orientation of the individual molecules. Accordingly, it is preferred to use hydrocarbons having branched chains and a symmetrically arranged hydrocarbon group. The frothers described include terpenes of various structures, pine oil which consists predominantly of terpene alcohols, for example terpinol, and also cresol and a number of synthetic frothers, such as for example methylisobutylcarbinol (MIBC) and triethoxybutane (TEB).
The optimal use of the frothers set forth above is determined not only by the separation problem to be solved, but also, as stated above, by the other components present in the pulp, such as collectors, regulators, etc.
Published German Application No. 19 30 671 describes a flotation based process for the separation of minerals from ore in an aqueous pulp in which air is introduced into the pulp containing a frother and separation of the valuable minerals is facilitated by means of the air bubbles formed. The frother used is a reaction product of ethylene oxide or propylene oxide with alcohols or glycols or lower alkyl monoethers thereof.
Published German Application No. 19 30 864 describes a process analogous to the process described in DE-OS No. 19 30 671, in which the frother used is the reaction product of ethylene oxide, propylene oxide or mixtures thereof with a monohydric alcohol containing at least three hydroxy groups in the molecule. The frothers disclosed in the two above-cited publications may be used both for the flotation of coal and for the flotation of a large number of ores and lead to a satisfactory discharge of the fractions which it is desired to enrich by the flotation process. Where conventional collectors are used, the frother was not observed to have any unfavorable effect on the properties of the collector in the flotation pulp. However, the selectivity of many separation processes was not entirely satisfactory, so that there is still a need for highly selective collectors which, in addition, lead to a high yield of the desired fraction.
In addition, EP-A No. 0 113 310 describes flotation processes for coal using frothers. The frothers used are reaction products of a monobasic or dibasic C.sub.1 -C.sub.10 carboxylic acid and a polyhydroxy compound, the resulting ester alcohols containing at least one free hydroxy group. Products containing branched alkyl groups which contain a total of 6 to 19 carbon atoms are disclosed as preferred in EP-A-0 113 310.